DE102007008104A1 - Process to regenerate sand pre-used in a metal casting process by burning and washing out organic and inorganic residues - Google Patents

Abstract

In a process to regenerate sand pre-used in a metal casting process and incorporating organic and/or inorganic core residues, the sane is regenerated by a combination of thermal and wet chemical stages. The core residues are crushed together with the hardened core sand, followed by burning out the residues and their removal by washing out inorganic binding agents. The washing solution and residues are drained from the sand. The clean casting sand is then classified prior to re-use.

Description

The The invention relates to a method for regenerating foundry sand or foundry used sand, which during the casting process is obtained using core, with the cores out of the Part organically bound and partly inorganic bound core sands are formed. The process comprises a combination of thermal and wet-chemical preparation.

In The metal foundry will be different depending on the requirements profile Molding bases and foundry core compositions.

Under In the following, the cores are individual cores, core packages, composites Cores or their combination to understand. The cores are going out Core sand formed. After pouring, the cores go in Foundry old sand over. A source for Altsand is the waste material produced prior to casting (eg. B. core breakage) or otherwise hardened core sand mixtures.

When Form base material is usually sand used, especially quartz sand, Chromite sand, zircon sand and olivine sand, the former being the largest Spread has. The Synthetic core sand mixtures exist in usually made from treated natural sand (clay content <1%) with binder additives. The treatment usually takes place from a cleaning, classification and drying.

in principle The basic materials for shape and core production differ Not. Variable here is the preparation and the transfer with binders.

For the casting cores or models become partly inorganic Binder used, since it has good strength properties above all (Others have compressive strength). Here one differentiates here Quellbinder and hydraulic binders. Source binders are Tonide. They harden by supplying heat and react relatively little with others Metal oxides.

Hydraulic binders are z. As water glass (sodium silicate, Na ₂ SiO ₃ ), cement or gypsum. Water glass can be cured, for example, with CO ₂ gassing, hot air rinsing or by dehydration.

to Production of organically bound cores becomes prevalent applied the cold box method. These include the core manufacturing processes, in which wet pourable mold base in cold core boxes hardened in short times at room temperature become. The cores are made of core sand and a two-component chemical binder (eg PUR). Hot-boxing procedures often use as binder liquid phenol, furan and amino resins, respectively their combinations, with the addition of a warm curing agent, such as z. B. ammonium stearate. The curing takes place, for example after firing in hot core boxes at temperatures of about 200 to 270 ° C.

Often is different for cost reasons in a casting process Sand used. The workpiece-near sand, in particular the Model sand often consists of a large proportion New sand. It is of great economic interest the highest possible proportions of recycled foundry sand to use.

From the EP 05 21 201 A1 a method for the regeneration of foundry sand is known, wherein the core sand as molding material inorganic binders such as bentonite or / and organic binders such as in particular phenolic and / or furan resins. It is intended to impregnate the old sand to be treated with water and then to dry in a moist fluidized bed in a heated fluidized bed.

From the DE 19925 720 C1 For example, a method and an apparatus for processing foundry sand is known. The foundry sand is conditioned after the transfer of the originating from the production process used sand by intermediate storage, admixture of virgin sand and admixture of aggregates, in particular binder, in such a way that the processed foundry sand is then processed into new forms. To improve the conditioning of the foundry sand, at least some of the aggregates are added to the foundry sand prior to intermediate storage.

by virtue of different requirements for the cores within a mold or differently operated casting lines can foundry sands in a foundry of inorganic and organically bound nuclei next to each other and incurred in variable amounts.

Problematic is the preparation of mixtures of inorganic and organic tied foundry old sands in a reusable Quality.

foundries are under pressure to reduce their emissions. The emissions are based to a large extent on organic core binders, which are mostly used in cold-box processes. In contrast Organic binders can be inorganic core binders (AOB) use almost zero emissions.

The introduction of AOB into existing casting Repairs with sand reclamation are difficult or not possible within the framework of normally existing process chains, as foundry sands with inorganic bonding and with organic bonding must not mix. In the case of mixing, a renewed production of organically bound cores, especially in the cold-box process would not be reliable. With recycling of the reclaimed core sand, the basicity of the resultant regenerated molding base inevitably increases steadily. This is an effect of the increasing content of inorganic binder or water glass binder. Both the processability or pot life, the mixed Fomsandmassen and the strength level of the formed cores would be insufficient, since the organic binder systems, especially cold-box bovine systems cure in the basic medium prematurely.

It It is therefore an object of the invention to provide a method for joint preparation of mixed foundry old sands and old sands organic and inorganically bound core sands that reuse the regenerated sands for both inorganic and for organically bound mandrels allows.

• a) Zerkleinerung der Kerne oder gehärteten Kernsande
• b) thermische Aufbereitung durch Ausbrennen der organischen Binder und Bestandteile
• c) nasschemische Aufbereitung durch Auswaschen des anorganischen Binders mit einer Waschlösung
• d) Abtrennung der Waschlösung und des in der Waschlösung gelösten und/oder suspendierten anorganischen Binders
• e) Trocknung und Klassierung des regenerierten Gießereisandes unter Bildung von Regeneratsand, mit den Merkmalen des Anspruchs 1.

The object is achieved by a method for regenerating foundry sand and / or used sand, which is obtained during casting using cores of organically bound and inorganic core sands, by a combination of thermal and wet chemical processing, with the method steps

• a) Crushing of the cores or hardened core sands
• b) thermal treatment by burning out the organic binder and constituents
• c) wet-chemical treatment by washing out the inorganic binder with a washing solution
• d) separation of the washing solution and the dissolved and / or suspended in the washing solution inorganic binder
• e) drying and classification of the regenerated foundry sand to form regenerated sand, having the features of claim 1.

The method according to the invention is particularly advantageous if inorganically bound cores or mandrels are already existing Foundries or foundry processes with sand regeneration be introduced by organically bound foundry cores.

Of the Use of the method according to the invention leaves the application of inorganic and organic bonded nuclei for the production of mixed core packages (inorganic and organic bound part cores). Likewise, in a foundry the Operation of different casting lines next to each other possible, in each case only one of the two core variants use without having maintained different regeneration procedures Need to become.

It is provided, the foundry sands or rest sands within the casting line or even different To collect casting roads and after passing a conventional sand grinder, such as a To convert tuber crushers into a thermal regeneration. This thermal regeneration serves to burn off the organic Ingredients. It is important that the inorganic Binder or inorganic constituents of the foundry association remain virtually unchanged while the organics are completely removed.

The Burning out of the organic components is preferably carried out at a Temperature below 900 ° C, typically at 500-900 ° C. Particularly preferred are temperatures in a range of 580-650 ° C. The burnout is preferably carried out in a fluidized bed reactor, especially at a temperature in the range of 580 to 650 ° C carried out.

ever If necessary, this is followed by dedusting the pre-regenerated Gießereialtsandes.

It is essential to the invention that after the thermal Regeneration a targeted separation of the remaining inorganic Binders is performed.

Of the thermally pre-regenerated foundry waste sand is now inventively one Wet regeneration (wet chemical treatment) supplied. in this connection is made by suitable washing with aqueous Solutions of Foundry Altsand from Inorganic Binding freed. The washes can through repeated circulation of the washing solution, possibly with different Press and speeds of wash water / wash solution performed become.

When Washing solution becomes water, optionally with additives, in particular for the regulation of the pH, the surface tension and the foaming used. It is preferred in the washing solution set a neutral pH, especially in use of silicate binders, such as water glass.

In a settling tank or basin, the rinsed inorganic binder is collected and separated. The binder can be at least partially recovered as a binder for new Kernformstoffmi use scraps.

Become several washes performed, it is preferred at least in the last wash, set a neutral pH. This effectively prevents basic reclaimed sand can arise.

Of the so regenerated foundry sand is subsequently dried. The waste heat is preferred during drying the first regeneration level used.

In a further process stage is provided the dried foundry sand to classify and break down into appropriate fractions.

By The Regeneratsand thus formed are the mold bases for the different casting cores, and core manufacturing processes made available. A mixing of different sands is thus possible.

Of the Regeneratsand can be with changing proportions of new sand as a molding material in the cold-box process (CB) or for the production of inorganic bonded cores (AOB) for core production reuse.

The Method is preferably applied to foundry processes, which work with composite cores or core packages which the mandrels are only partially made by the cold box process become.

Example:

For checking the effectiveness of the method were comparative experiments with standard specimens made of reclaimed sand (Reg. AOB / CB) and new sand.

When Yardstick for comparing the sands was the strength (flexural strength) and strength after different processing times (from organic bound standard specimens used.

to Production of standard test specimens according to the invention Processes were foundry sands from a cold-box process (CB) and inorganic bound sands (AOB) in a ratio mixed by 50/50.

These Mixture was for thermal regeneration for 3 h Heated to 600 ° C. The wet-chemical regeneration took place by washing 5 times with water without additives. This was done drying at 120 ° C. From this regenerated foundry sand were using cold box binders standard test specimens manufactured and their strength after certain periods of storage measured.

The Comparison bodies were from the corresponding new sand made with the same binder.

1 shows the increase in strength of the standard test specimens after different storage periods.

It shows that for test specimens made of new sand and for Regeneratsand with increasing storage time an increase the flexural strength results. For all storage times are regenerated Core sand and new sand almost at the same strength level.

2 shows the strength of the standard test specimens of virgin sand and regenerated material after different processing times.

It shows that both new sand and regenerated sand almost the same permanent strength depending on the processing time exhibit. The regenerated sand test specimens show in terms of measurement accuracy, the same strengths as the New sand test specimen on.

Both Unexamination results show that with the regenerated sand of inorganic and organic bonded sand provided a molding base which equals a new and untreated new sand is.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• EP 0521201 A1 [0010]
• - DE 19925720 C1 [0011]

Claims (11)

Process for regenerating foundry waste sand and / or used sand, which is used in the casting process from nuclei of organically bound and inorganically bound core sands, by a combination of thermal and wet-chemical processing, with the process steps a) crushing of the kernels or hardened core sands to form foundry used sand and / or used sand b) thermal treatment of foundry waste sand and / or Altsand by burnout of organic binders and ingredients c) wet-chemical treatment by washing out of the inorganic binder with a washing solution d) separation of the washing solution and that dissolved and / or suspended in the wash solution inorganic binder e) drying and classification of the regenerated Foundry sand with the formation of regenerated sand. Method according to claim 1, characterized in that that in step c) a neutral pH is set. Method according to claim 1 or 2, characterized that after step c) or d) a neutralization of the washing solution he follows. Method according to one of the preceding claims, characterized in that between steps b) and c) a Dedusting of the pre-regenerated foundry sand takes place. Method according to one of the preceding claims, characterized in that the wet regeneration by repeated Circulation of the washing solution, in particular with different pressures and speeds. Method according to one of the preceding claims, characterized in that dissolved in the washing solution or suspended inorganic binder collected and at least partly as a binder of the dosage for new core compound mixtures is fed again. Method according to one of the preceding claims, characterized in that the burnout of the organic components at a temperature below 900 ° C takes place. Method according to one of the preceding claims, characterized in that the burnout of the organic components in a fluidized bed reactor at a temperature in the range of 580 to 650 ° C takes place. Method according to one of the preceding claims, characterized in that substantially as inorganic binder find silicate binders use. Method according to one of the preceding claims, characterized in that the regenerated foundry sand is reused as core sand in the cold box process. Process for the production of foundry cores after the cold-box process, characterized in that a after used in claims 1 to 9 Regeneratsand becomes.